The FDA has accepted for priority review a supplemental biologics license application (sBLA) for intravenous (IV) efgartigimod alfa-fcab (Vyvgart) to treat adults with acetylcholine receptor antibody (AChR-Ab) seronegative generalized myasthenia gravis (gMG), potentially offering a new option for a challenging-to-treat condition. The agency granted the application a Prescription Drug User Fee Act (PDUFA) target action date of May 10, 2026.1
What Are IV Efgartigimod and Generalized Myasthenia Gravis?
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IV efgartigimod is a first-in-class neonatal Fc receptor antagonist already approved for gMG in patients who *do* have detectable acetylcholine receptor antibodies. Generalized myasthenia gravis (gMG) is a chronic autoimmune neuromuscular disease causing muscle weakness that worsens with activity and improves with rest. It affects adults and can significantly impact daily life.1,2
Approximately 80% of those with gMG test positive for antibodies against the acetylcholine receptor (AChR), categorized as AChR-Ab seropositive gMG. However, around 20% test negative for these antibodies, falling into the AChR-Ab seronegative category.1
What Clinical Data Supported This Action?
The sBLA is based on data from the phase 3 ADAPT SERON clinical trial (NCT06298552)3, a randomized, double-blind, placebo-controlled study conducted across North America, Europe, China, and the Middle East. The trial evaluated the safety and efficacy of IV efgartigimod in adults with AChR-Ab seronegative gMG, including those with muscle-specific tyrosine kinase-positive (MuSK+), low-density lipoprotein receptor-related protein-positive (LRP4+), and triple seronegative subtypes.
A total of 119 patients participated, split into two parts. Part A randomized patients to receive either four weekly infusions of IV efgartigimod or a placebo, followed by a five-week follow-up. Part B was an open-label extension where participants received additional cycles of infusions based on their clinical status. All participants were already receiving at least one gMG treatment, such as acetylcholinesterase inhibitors, corticosteroids, or immunosuppressants.3,4
The primary goal of the trial was to measure the change in Myasthenia Gravis Activities of Daily Living (MG-ADL) total score from the start of treatment to day 29 (part A). Researchers also tracked changes using the Quantitative Myasthenia Gravis (QMG), Myasthenia Gravis Quality of Life-15 revised (MG-QoL 15r), Myasthenia Gravis Composite (MGC), and EQ-5D-5L VAS scales.3
The ADAPT SERON trial successfully met its primary endpoint (P = .0068), demonstrating a statistically significant improvement in MG-ADL total score compared to placebo after four weeks. Patients treated with IV efgartigimod showed a clinically meaningful 3.35-point improvement in MG-ADL total score at week four. Improvements in MG-ADL and QMG scores were sustained across treatment cycles and observed in all patient subgroups.1
IV efgartigimod generally appeared well-tolerated, with a safety profile consistent with previous findings in patients with AChR-Ab seropositive gMG. No new safety concerns were identified.1
About the Trial
Trial Name: A Phase 3 Study to Evaluate the Efficacy and Safety of Efgartigimod IV in Patients With Acetylcholine Receptor Binding Antibody Seronegative Generalized Myasthenia Gravis (ADAPT SERON)
ClinicalTrials.gov ID: NCT06298552
Completion Date (Estimated): June 2027
The manufacturer advises against using IV efgartigimod in patients with a known serious allergy to efgartigimod alfa or any of its components. The drug may also cause serious allergic reactions and a drop in blood pressure.1
“Patients living with seronegative gMG continue to face limited treatment options, and there remains a significant need to meaningfully improve their lives,” said Luc Truyen, MD, PhD, chief medical officer. “The FDA’s acceptance of our sBLA with Priority Review status reflects the potential of [IV efgartigimod] to address this need. We look forward to continuing our dialogue with the FDA as they review our application.”1
